Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. Which of the following is not a desirable property of a refrigerant?

Low boiling point

High risibility with oil

Good electrical conductor

Large latent heat

2. The operating pressure for refrigerating units using R-12 as a refrigerant is

15 bar

8 bar

2 bar

30 bar

3. The vapour compression refrigerator employs the following cycle

Rankine

Carnot

Reversed Rankine

Reversed Carnot

4. The minimum temperature to which water can be cooled in a cooling tower is

Dew point temperature of air

Wet bulb temperature of air

Dry bulb temperature of air

Ambient air temperature

5. The bank of tubes at the back of domestic refrigerator is

Capillary tubes

Refrigerant cooling tubes

Condenser tubes

Evaporator tubes

6. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Less

Unpredictable

7. The value of C.O.P in vapour compression cycle is usually

Always less than unity

Always more than unity

Equal to unity

Any one of the above

8. A thermostatic expansion valve in a refrigeration system

None of the above

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

9. For obtaining high COP, the pressure range of compressor should be

Optimum

Low

Any value

High

10. Critical temperature is the temperature above which

A gas will immediately liquefy

Water will never evaporate

Water will evaporate

A gas will never liquefy

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11. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant pressure

Takes place at constant entropy

Takes place at constant temperature

Involves no change in volume

12. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Negative

None of these

Zero

Positive

13. The freezing point of sulphur dioxide is

-77.7°C

-56.6°C

-135.8°C

-75.2°C

14. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(B) Heat stored in the human body

(D) Difference of (A) and (B)

(A) Heat dissipated to the surroundings

15. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

5.12

2.15

16. Which of the following cycles uses air as the refrigerant?

Carnot

Bell Coleman

Stirling

Ericson

17. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Brine

Freon

Ammonia

Carbon dioxide

18. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

Less

More for small capacity and less for high capacity

19. Rating of a domestic refrigerator is of the order of

0.1 ton

10 tons

5 tons

40 tons

20. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Sub-cooling or under-cooling

Super-cooling

None of these

Normal cooling

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21. The condition of refrigerant after passing through the condenser in a vapour compression system is

Saturated liquid

Superheated vapour

Wet vapour

Dry saturated vapour

22. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 3

1: 9

9: 1

1: 1

23. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₁ / (T₂ - T₁)

(T₁ - T₂)/T₁

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

24. The domestic refrigerator uses following type of compressor

Piston type reciprocating

Miniature sealed unit

Centrifugal

Axial

25. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

2.33

1.33

3.33

4.33

26. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

27. The boiling point of ammonia is

-33.3°C

-10.5°C

-30°C

-77.7°C

28. A bootstrap air cooling system has

Two heat exchangers

Four heat exchangers

Three heat exchangers

One heat exchanger

29. The capillary tube, as an expansion device, is used in

All of these

Water coolers

Room air conditioners

Domestic refrigerators

30. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect vapours

Superheat the vapour

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

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31. The curved lines on a psychrometric chart indicates

Dew point temperature

Dry bulb temperature

Wet bulb temperature

Relative humidity

32. In a refrigeration system, the expansion device is connected between the

Receiver and evaporator

Evaporator and compressor

Compressor and condenser

Condenser and receiver

33. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

34. In a lithium bromide absorption refrigeration system

Water is used as a refrigerant and lithium bromide as an absorbent

None of these

Lithium bromide is used as a refrigerant and water as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

35. Freon group of refrigerants are

Inflammable

Non-inflammable and toxic

Nontoxic and non-inflammable

Toxic

36. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

At critical Temperature

Much below critical temperature

Above critical temperature

37. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.376

0.4

0.67

0.6

38. Which of the following statement is correct?

(D) Both (A) and (B)

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(B) The increase in air movement increases the evaporation from the human body.

39. Cooling water is required for following equipment in ammonia absorption plant

Condenser

Condenser, absorber and separator (rectifier)

Absorber

Evaporator

40. Most thermostatic expansion valves are set for a superheat of

10°C

5°C

20°C

15°C

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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